This invention in general concerns cargo vehicles and in particular lorries or trucks having a semi-trailer or trailer, i.e. vehicles of the type that comprises a pulling vehicle having a trailer mounted, or a so-called tractor and a semi-trailer attached thereto. Although the invention is defined to concern trucks or lorries it will be obvious to persons skilled in the art that also vehicles for transporting persons, for example busses, may be designed in accordance with the teaching of the present invention so the invention is also to comprise the use of the invention within such closely related and technically equivalent areas. More particularly, the invention concerns a technique whereby the maneuvering abilities of such vehicles is improved without traffic safety being deteriorated.
The invention particularly concerns a system for guiding at least one set of rear wheels on a semi-trailer or trailer of a cargo vehicle, which comprises said semi-trailer or trailer and a truck trailer or tractor, and comprising
bearing means in which said rear wheels are journalled rotatably with respect to the chassis of the semi-trailer or trailer so that said rear wheels can turn from neutral position, in which the rear wheels generate no steering effect, to one side in order to generate steering of the vehicle in one direction with respect to said neutral position, or to the other side side in order to generate steering of the vehicle in the opposite direction with respect to said neutral position, PA1 power generating means adapted to affect said rear wheels and, when activated, to generate said turning of said rear wheels to one or the other side, PA1 activation means, mounted in the cabin of the vehicle and adapted to be operated by the driver of the vehicle for activating one of the power generating means and for generating steering of said at least one set of rear wheels independently of the steering of the truck trailer or tractor, and PA1 locking means adapted to be operated from the driver's cabin of the vehicle for generating, in a first position locking of said rear wheels in said neutral position, and being switchable from said first position to a second position, in which the rear wheels are released and may be brought to turn by activation of the activation means.
Systems of this kind are known within the art, more particularly from the following patents, U.S. Pat. No. 5,213,353, U.S. Pat. No. 5,035,439 U.S. Pat. No. 2,930,631 and FR 2,645,105. These publications disclose systems of the kind stated above as well as components for such systems. As described in for example U.S. Pat. No. 5,035,439 these systems are operated by the driver of the vehicle, in which the system is mounted, activating a switch, which is connected to the locking means, and which by activation switches the locking means from the first position to the second position, upon which it is possible for the driver to generate the turning of the guided steering rear wheels by activating the activation means. By generating the guided steering of the rear wheels a substantial reduction of the total turning diameter is generated, as realized in the said prior art, which, during forwards or backwards driving, enables the vehicle to turn round even very sharp corners and thus maneuver at a very limited area, including maneuvering in an area considerably smaller than what is required for maneuvering a similar vehicle having no guided steering system, for instance to turn round a sharp corner, back up to a loading ramp, turn in a limited area etc. It will be evident to persons skilled in the art, however, that a reduction in the turning diameter to such a substantial extent as achieved by a guided steering system of the this art necessarily entails instability in driving at normal speed on a road and thereby entails a safety risk not only to the driver of the vehicle but also for other persons in the traffic in case the driver activates the guided steering system when driving on a normal road and brings the vehicle to turn very sharply and thereby provokes a considerable risk of said vehicle turning over or loosing its steering capability because of skidding.
It should be noted that in connection with a different technique, i.e. co-steering on trucks or busses, safety systems are known, but said co-steering systems, which are described in for example EP 0 710 601 and DK 94 00327 U3 differ from the guided steering system in that the rear wheels of the vehicle perform co-steering corresponding to the steering deflection brought about by means of the steering wheel of the vehicle and thus corresponding to the steering front wheel of the pulling vehicle or the truck. Consequently, co-steering systems of said type have no activation means which are operated from the driver's cabin of the vehicle and may generate steering, i.e. a guided steering of the rear wheels. Co-steering systems of said type provide interconnection between the co-steering rear wheels and the steering front wheels and comprise locking means corresponding to the locking means of the guided steering system described in the preamble of this description and they may furthermore comprise a speed related locking and corresponding return facility of the co-steering rear wheels when the vehicle moves at a speed exceeding a preset limited speed level, typically a speed of the order of 50 km/h as described in EP 0 710 601.
The basis of the present invention, consequently, lies in realizing that known guided steering systems in spite of their excellent qualities in improved maneuvering may entail a safety risk to the driver of the truck in question as well as to other persons in the surrounding traffic in case the driver intentionally or unintentionally activates the system for guided steering of the rear wheels of the truck when driving on an ordinary road and at normal speed.